Electrical motor control system



Marh 13, 1951 H. zlEBoLz ETAL ELECTRICAL MTR CONTROL SYSTEM Filed March13, 1946 tijd,

Patented Mar. 13, 1951 ELECTRICAL MOTOR CONTROL SYSTEM Herbert Ziebolzand Paul Glass, Chicago, Ill., assignors to Askama. Regulator Company,Chicago, Ill., a corporation of Illinois Application March 13, 1946,serial No. 654,050

(o1. sis-30) 6 Claims. 1

The invention relates generally to an electrical control circuit andmore particularly to a circuit for controlling the movement of a membersuch as the carriage of a machine tool, the hook of a hoist, the beam ofa crane, or the like.

A general object of the invention is to provide a new and improvedelectrical system for controlling a member so as to effect a rapidmovement of the member from one position to another while accuratelypositioning the member in its new position.

Another object is to provide a new and improved electrical system forrapidly moving a member from one position to another while accuratelypositioning the member in its new position, in which the system isindependent of the characteristics of the particular electric motoremployed to drive the member and is also independent of the nature ofthe load provided by the member.

Another object is to provide an electrical systern for controlling amovable member employingY a combination of speed control and positioncontrol.

Still another object is to provide an electrical system for controllinga movable member having means utilizing the speed of movement of themember for rough control of the member and means utilizing the positionof the member for a ine control and nnal and accurate positioning of themember.

A further object is to provide an electrical system for controlling amovable member having a first control means for rough control of themember and a second control means for fine control of the member, saidsecond control means being inoperative while said first control means isbeing employed but being maintained in precisely related position withthe controlled member and operable at the will of an attendant to takeover control of the member from the first control means.

A further object is to provide an electrical system for controlling amovable member having a first control means for causing movement of themember in either of two directions and at any speed within the range ofspeeds of the power means driving the member, this first control meansbeing operable to control the speed of the member only; and a secondcontrol means operable to take over control from said first means in anyposition of the member, this second control means governing the positionof the member and causing the member accurately to follow the movementof a manual control element.

Other objects and advantages will become ap-` parent from the followingdetailed description taken in connection with the accompanying drawings,in which:

Fig. l is a block type circuit diagram of a sys- Y tem embodying thefeatures of this invention.

Fig. 2 is a block type circuit diagram showing a modified form of theinvention.

While the invention is susceptible -of various modifications andalternative constructions, it is shown in the drawings and willhereinafter be described in a preferred form and one modification. It isnot intended, however, that the invention is to be limited thereby tothe specific disclosures made. On the contrary, it is intended to coverall modifications and alternative constructions falling within thespirit and scope of the invention as defined in the appended claims.

As above stated, there are many industrial applications in which it isdesirable that a movable member be so controlled that it may be quicklymoved from one position to an approxi mately new position and thenprecisely positioned and held in the new position. By way of exemplarydisclosure, the invention herein will be described as employed for thecontrol of a hoist, for in such an application in particular there isusually need for moving the load-carrying member of the hoist throughconsiderable distances and yet it is frequently necessary, particularlywhere the hoist is employed in assembly work, that the object carried bythe hoist be very slowly lowered to assume a very precise position withrespect to some other part of the product being assembled. Such a hoistis diagrammatically represented in Fig. 1 b, the general referencecharacter 4, with the element more particularly representing a winch ordrum xedly mounted on a shaft 6 and having wound thereon a cable or likemeans 'l carrying at its free end an electromagnet, grapple hook, orother means represented at 8 and constituting the member whose movementsand position are to be controlled. The hoist, more particularly theshaft 6 thereof, is driven by an electric motor 9 preferably andcommonly through suitable gearing I 0 interposed between the hoist shaft6 and the motor shaft Il. The motor and the gearing together constitutereversible and variable power means for driving the shaft B of therhoist at varying speeds in either direction of rotation. Normally themotor 9 will -be, and is herein, a reversible, variable speed motor butit is not to be understood that it must necessarily be so. Contemplatedas alternative constructions would be the employment of gearingadaptable to reverse the direction of rotation of the hoist shaft 6though the motor shaft Il may always rotate in one direction; and alsocontemplated is the possibility that the hoist motor may operate atconstant speed with variation in hoist `shaft speed as well as direction-being effected through control of the gearing ID.

To control the motor Bso as to obtain the ob* Jectives of thisinvention, the control system conm prises generally a rst control meanswhich governs the speed of movement of the controlled member 3. Thismeans includes a manual control element I2 and is operable in accordancewith the direction and extent of movement of this manual control elementfrom anormal position to govern the direction and speed at which thecontrolled member 8 is driven, independently of the distance throughwhich themember isto be driven. This control means utilizes the speed.of movement of the controlled-memberlasthe counteracting control signaland 'is Suitable and utilized for rough control and positioning of themember 3 only. It will'in the balance of the specication and vin theclaims be referred to as speed control means. f

A second control means is provided for-governing movement of the member8 for its iinal and accurate positioning. This control meanswill in thebalance of the specification and in the claims be referred to asposition control meansl It includes a second manual control element I3and is operable at the will of the attendant to take over control of thehoist from the speed control meansk and to cause the controlled member 8to have a movement and to take up a position corresponding precisely tothat of the manual control element I3. The position control meansutilizes the position of the controlled member 8 as distinguished fromthe speed thereof as the counteracting control signal and thus assuresaccurate and precise positioning of the controlled member.

Though the position control means is idle and ineffective while thespeed control means is exercising its control, it is a feature of thisinvention that portions of the position control means are maintained inprecisely coordinated relationship with the controlled member 8 and thusare at all times and in any position of the controlled member 8 operableto take over control of the member 8.

Turning now particularly to the form of the invention shown in Fig. 1,the speed control means comprises the manual control element I2 alreadymentioned. This element is, through the medium of a shaft Iii, forexample, xedly associated with the movable contact I5 of a potentiometerI6, herein shown as having .its opposite ends connected. throughterminals II to an alternating current voltage source. The midpoint I8of the potentiometer I6 is by a lead I9 connected to one ber 8. Thismeans is herein shown as a pilot generator driven directly from themotor shaft II and connected by leads 25 and 2S to have an inversefeed-back relationship with the signals 'generated by the potentiometerI6. The signal generated by the means 24 will hereinafter be referred tolas the operation indicating or pilot signal, and the signal resultingfrom a combination of the mam signal and the pilot signal will be knownand referred to as the control signal. The-lead-2` is here shownconnected to a blade 21 of th'e'switch 2l adapted in one position tomake contact with the contact 23. A second blade 28 is adapted to makecontact with the contact Zand this blade is by-a-lead 29 connected to anamplifier St as is also the lead 25. The amplifier may be of any wellknown construction capable of responding to an alternating currentsignal of varying magnitude and operating to produce a signal of acharacter and magnitude suitable and capable of controlling the speedand direction of rotation of the motor il. Herein the amplier 30 isshown as controlling the motor 9 through a reactor means 3| it beingunderstood that the disclosure of reactor means herein is merely toindicate the desirabliity thereof and not the indispensability. Thespeed control means operates as more particularly disclosed in theSoller et al. application, Serial No. 569,476, filed December 23, 1944,to drive the hoist IIJ in a direction and at a speed called for byadjustment of the manual control element I2. This speed is veryaccurately maintained for the magnitude of @the control signal is inpart determined by the speed at which the hoist is being operated and ifthat speed becomes too great the control signal is diminished, and,conversely, if the speed is not great enough the control signal isincreased. As a result, the speed is maintained at the speed called forby the adjustment of the control element I2, and the speed at which themember 8 is driven is in no way related, at any time during such drive,to the distance of the member from its intended position at the selectedtermination of the traversing drive period.

The position control means includes the manual control element i3already mentioned and additionally includes means operable to cause the,hoist accurately and precisely to follow the movestationary Contact 2of a multiple blade` switch Y 2l.A The movable contact I5 ofthepotentiometer isby a lead 22 connected to a second stationary contact 23of the switch 2|. The potentiometer functions in well known manner underthe control of the element I2 to produce an alternating current signalof opposite phase as the control element I2 is swung in onedirection orthe opposite directionfrom its normal position, so as to determine thedirection of movement of the conments of and to assume a positioncorresponding to that of the control element I3. This means alsoincludes devices whereby the control means is normally idling orineffective but is operable at .the will of the attendant to wrestcontrol from trolled member 8; and likewise functions to prothe speedcontrol means. In order that the position control means may be operativeto take over control at any time and in any position of the hoist, it isarranged to have a part thereof maintained in precise positionalrelationship with the hoist. This latter part, speaking generally, in-

cludes a plurality of electrical devices one of which is associated withthe hoist and, during the control of the hoist by the speed controlmeans, serves as a master controlling a second electrical device locatedat the control station to maintain this positional relationship'withrespect to the hoist. The position control means is such that thissecond electrical device, during the control of the hoist by theposition control portional tothe speed of movement. of 4the .con-

trolled member-.8 and of'a phase'depending upon. the direction ofmovement of the controlled mem- -\..ter'slave relationship are Selsynsofwhich herein i three are employed, a Selsyn control transfer 32,

5. a Selsyn motor 33 and a Selsyn generator 34. The latter of these isoperatively connected with the shait 3 of the hoist so as to partake ofthe same rotation as the shaft and this Selsyn constitutes the masterduring the time that the speed control means is governing the hoist. TheSelsyn is adapted for receiving energization from an alternating currentvoltage source represented at 35 and has three leads 3l connected toblades 31 forming a part of the switch 2|. The switch 2| is operabethrough the, blades 31 electrically to connect the Selsyn 34 with eitherthe Selsyn 32 or the Selsyn 33 and, to that end, has

A two sets of contacts or terminals 38 and 39 of three terminals each.The terminals of the rst set 33 are by leads 43 connected to Selsyn 32and the terminals of the set 33 are by leads 4| connected to the Selsyn33. The Selsyn 33 is adapted for energization from an a'ternatingcurrent voltage source represented at 42 and Selsyn 32 is by leads 43connected to stationary contacts or terminals 44 associated with theblades 21 and 23.

The rotors of the Selsyns 32 and 33 are connected together by a shaft 45and are in turn, through a shaft 43, connected to one element 41 of aclutch, generally designated CL. The other element 48 of the clutch isby a shaft 49 connected with the manual control element I3.

Both the clutch CL and the switch 2| are electrically actuated and, tothat end, the clutch has an actuating coil 53 and the switch 2| has anactuating coil connected in series in a circuit 52 having also in seriesa suitable voltage source 53 and a switch 54 which is located on thecontrol element |3 and which must be actuated before the control elementcan be rotated. In the normal position, that is, when the actuating coil53 is not energized, the clutch CL is open and the switch 2i is in itsupper position, that is, with the blades 28 and 21 making Contact,respectively, with the stationary contacts 23 and 23 and with the blades31 making contact with the terminals or stationary contacts 39. Uponclosure of the switch 5t, the clutch CL wi-l be engaged and the switch2l will be shifted to its down position in which the blades 23 and 21now make Contact with the terminals 44 and the blades 31 make contactwith the terminals 33. It will be appreciated that the blades of theswitch 2| are interconnected by a common shaft 55.

To aid in giving an understanding of this invention, the operationthereof will be briey described. Let it be assumed that the hoist is ina vraised position and that it is carrying a load which is to be loweredto a precise, lower position and that the distance through which theload is to be moved is considerable. Under those circumstances, theoperator or attendant would grasp the manual contro element I2 and swingthe same counterclockwise, as viewed in Fig. l, thereby causing thegeneration of a main signal calling for a lowering of the hoist.Dep-ending upon the extent or angle through which the control element I2is rotated, the hoist would be driven at a slow speed or at the fullspeed of the motor 3. Normal`y the operator would swing the controlhandle l2 at a moderate rate, thereby permitting the hoist to have anormal acceleration and, after that normal acceleration, to reach andremain at full speed of the motor 3. Under this speed control, thedistance through which the hoist travels is, of course, determinedentirely by the rate at which it is driven multiplied by the length oftime that it is driven at that rate.. IIvhus, after a given intervaloftime, and

as the load carried by the hoist approaches its desired final position,the attendant swings the control element i2 in the opposite directiondecelerating the hoist and eventually bringing the load carried by thehoist to rest removed a short distance from its final position. The nalposition can be quite closely approximated for, after all, the speedcontrol is capable of causing the motor to operate at any speed fromfull speed down to Zero and, inasmuch as the final control signal is inpart determined by the pilot signal that is generated by the pilotgenerator 24, the system is stable in operation.

During this control by the speed control means, the Selsyn 34 has, ofcourse, been driven by the hoist shaft 6 and, since it has beenelectrically connected with Selsyn 33, the latter has remained inequivalent phase position with Selsyn 34 and hence with the shaft 3.Selsyn 32 has during this period been electrically disconnected but,inasmuch as it is physically connected through the shaft 45 with Selsyn33, its rotor too has been maintained in definite positionalrelationship with respect to the shaft 3 of the hoist. It is pointed outat this time that Selsyn 32 and Selsyn 33 are connected physically so asto have their rotors displaced 9G". The reason for this will be readilyunderstood by those skilled in the art. When the Selsyns 33 and 33 areconnected, the end sought and the result obtained is the maintenance ofa physical relationship between the Selsyns 33 and 34, hence torque forrotating the rotor of Selsyn 33. When the Selsyns 32 and 33 areconnected, the end sought is the obtaining of a signal from Selsyn 32calling for operation of the hoist motor in a particular direction ifthe position of the hoist does not correspond to the position of therotor of Selsyn 32. As a consequence, when the Selsyns 32 and 34 areelectrically connected and the rotor of Selsyn 32 bears thatrelationship to Selsyn 34 which is maintained when Selsyn 33 iselectrically connected to Selsyn 34 and is driven thereby, the signalgenerated by Selsyn 32 will be zero. Upon any departure from the abovecondition, a signal of other than zero magnitude and of a characterdepending upon the direction of departure will be generated.

To drive the hoist through the remaining short distance necessary toplace the load in precise position, commonly known as inching, theattendant now turns to the position control means, grasps the controlelement i3 and closes the switch 54. Such closure of the switch 54simultaneously engages the clutch CL coupling the control element i3 tothe rotor of Selsyn 32 and shifts switch 2| to its lower position inwhich the blades 21 and 28 now make contact with the stationary contacts44 and the blades 31 now contact with the stationary contacts 38. Selsyn32 is now electrically connected with Selsyn 34 and is, moreover,electrically connected with the control signal amplifier 33 of the speedcontrol means. The control element i3 is now rotated counterolockwise,as viewed in Fig. 1, and the hoist follows such movement precisely. Withrotation of the control element I3, the rotor of Selsyn 32 is, ofcourse, rotated and thus the phase relationship between it and Selsyn 34is changed and a signal is generated calling for lowering of the hoist.This signal will be gradually reduced and completely wiped out asoperation of the hoist rotates the rotor of Selsyn 34 and eventuallycauses it to have such a phase relationship with respect to Selsyn 32that the signal is completely audace When the attendant again wishes toraise the hoist, he simply opens the switch which disengages the clutchCL and restores the switch 2| to its normal up position. It is to beappreciated that the clutch CL is biased to disengaged position, theswitch 2i is biased to up position, and the control element I2 is biasedto its neutral or zero position. The speed control means thus is againin control and the hoist may be raised at any desired speed by swingingthe control element i2 clockwise, as viewed in Fig. l.

In the modified form of the invention shown for exemplary purposes inFig. 2, the hoist is still represented generally by the referencecharacter 4. The hoist comprises generally a drum or winch 5 fixed on ashaft e and having a cable or the like l" wound about the drum andcarrying at its free end a member Si. The member 8 is the member whosepositionis to be con trolled and may, of course, represent anelectromagnet, a grapple hook, or the like. Power means is provided fordriving the shaft 5 in opposit-e directions and at varying speeds andherein includes an electric motor il and gearing it. While the motor andthe gearing may vary so that adjustment of one or the other` may bringabout reversal in the direction oic rotation of the shaft 6 and thedriving thereof at varying speeds, these adjustments are hereaccomplished through the employment oi a reversible, variable speedmotor. As in the first form of the invention, the hoist is controlled bymeans which will hereinafter be referred to as speed cont-rol means andby other means which will hereinafter be referred to as position controlmeans, though in this form of the invention the speed control meanstakes the form of a stepped-up or speeded-up position control means.

More particularly, the control system comfprises signal generating meansoperable to produce a signal of opposite phase so as to determine thedirection oi rotation in which the shaft 6' is driven. rihis signalgenerating means herein is composed of a pair of Selsyns te and Si. TheSelsyn @il is by a pair oi leads 62 connected to an amplifier G3 in turnelectrically connected with the motor 9 and functioning to amplify andotherwise condition the signal so as to render it capable of controllingthe motor e. The Selsyn ii is also by a plurality of leads 6d connectedto the Selsyn Si which is energized from a suitable voltage sourcerepresen-ted at 65. The Selsyn di has its rotor mechanically connectedwith the shaft S so as to partake of the direction and extent ofrotation of that shaft. it will be readily understood to those skilledin the art that whenever, due to any cause whatsoever, the

rotors of the two Selsyns are out of step a sig-A It is readily seenthat Selsyn Si) is the master and that depending upon the direction andextent of rotation given to its rotor the hoist will be like-A wisedriven until the rotor of Selsyn 6i is again in step with the rotor ofthe master Selsyn 60. Alternately employable means are provided forrotating the rotor of Selsyn Sli and depending upon the speed at whichthe rotor is driven the system is employable either for speed control orfor ne and accurate position control. The a1- ternately employable meanscomprises a con-y stant speed motor 6G and a hand wheel 61. The latteris nonrot-atably aiXed to the input shaft 68 of a reversible andvariable transmission 69 having an output shaft 'i connected to therotor of the master Selsyn 68. A clutch CL' is adapted to couple oruncouple the constant speed motor from the shaft 68. The clutch CL' iselectrically controlled and to that end has associated therewith anelectrical control coil or solenoid El connected in series with amanually actuable switch 'i2 in a clutch control circuit 13. The clutchCL is adapted to be in disengaged position when the switch 'i2 is openand to be in engaged or coupled position when the switch 'l2 is closed.

The transmission 69 has a manual control element 'i4 which has a neutralor zero position and may be swung to either side of its neutralposition. In neutral there is no transmission of rotation whatsoeverfrom the input shaft 68 to the output shaft ill. As the control element14 is swung to either side of neutral position, transmission of rotationbetween the shafts 68 and 10 does take place and the direction in whichthe shaft 1D is rotated depends upon the direction from neutral in whicht-he control element lli is swung and the speed of rotation for anygiven speed of the shaft 58 also increases as the control element 14 isswung through a progressively greater angle away from its neutralposition.

It may aid the understanding of this invention brieily to describe theoperation. Let it be assumed, therefore, that the switch l2 is open andthat, accordingly, the clutch CL is disengaged. Under this arrangement,the input shaft 68 of the transmission 69 can be rotated only from thehand wheel 61, and the signal output of the Selsyn system is of anamplitude proportional to degree of error between actual and intendedpositions or" the driven member. If now the operator or attendant swingsthe control element 1 4 in either direction from its neutral positionand then rotates the hand wheel 6l, the rotor of the Y master Selsyn 60will, of course, be rotated and will then become out of step with therotor of the Selsyn 6l, thereby setting up a signal of a certaincharacter calling for movement of the hoist in one direction, at a speeddetermined by the speed of rotation of the master Selsyn rotor, andwholly independent of the length of time during which such drive is tobe maintained, or the distance of the member from the position which itis to have at termination 0f such drive. 1f the control element 'I4 isbut slightly displaced from its neutral position, the ratio betweenrotations of the shaft 68 and the shaft 'iii will, of course, be largeand thus an extremely fine control of the hoist is attained. If thecontrol element 'M is swung to its extreme in either direction from itsneutral position the ratio between rotation of the shaft 68 and shaft 10may, depending upon the nature of the transmission, be 1:1 or even ahigher factor. It will be apparent that, nevertheless, through the favorof the motor 66.

'medium of thev hand Wheel'l very accurate control of the Aposition ofthe hoist is still attainable.

Where it is desirable to move the hoist through a considerable distanceand hence where it is a saving of time to drive the same at a ratherhigh rate of speed, the hand wheel 6l is abandoned in Accordingly, theswitch l2 is closed energizing the coil 'Il and engaging the clutch CL'.As a result, the input shaft S8 of the transmission 8S is now driven atthe speed of the motor 66. Through manipulation of the control elementld, the attendant may now drive the rotoi' of the Selsyn SU in eitherdirection and at any desired speed from zero to some speed above orbelow the constant speed oi the motor B depending upon the ratiomaintained betweenv the shafts B8 and 'd when the control element liliris in either of its extreme positions.

We claim asour invention:

l. A control system for governing the movement of a member comprisingelectrically controlled-power means for driving the member at varyingspeeds in either of two opposed directions, an amplifier circuit forreceiving a contiol signal and rendering the same suitable to controlsaid power means, and control means for generating electrical signals towhich said amplifier circuit responds including a plurality of manuallyand independently operable signal sources having separate outputs, oneof said signal sources being arranged to produce a signal having a,distance representing value proportional to degree oferror betweenactualand intended positions of said member for accurate positioning, ofthe member, the other being arranged to produce a signal having a speedproducing value proportional to intended speed of drive through anindeterminate distance for traversing the member, and switching meanshaving a rst and second positions respectively connecting said outputsto said amplifier circuit. 2. A control system for governing themovement of a member comprising electrically controlled power means fordriving the member at varying speeds in either of two opposeddirections, an ampliiier circuit for receiving a control signal andrendering the same suitable to control said power means, and controlmeans for generating electrical signals to which said amplifier circuitresponds including a iirst Selsyn driven to have a direction and extentof movement corresponding to that of the member to be controlled, asecond Selsyn electrically connected with said iirst Selsyn forproducing a position error signal and with said amplifier circuit toapply such signal to the am'plier control input, manual means forrotating said second Selsyn to produce such a position error signal forinching control of the member, and means for taking over control fromsaid manual means and producing e, speed error signal for controllingthe drive of the member at higher rates including a manually operableelement for determining the direction and rate of movement of themember, and electrical means eiective during control by said secondcontrol means and responsive to operation of said -power means tomaintain said second Selsyn in positional correspondence with such amember.

3. A control system for governing the movement of a member comprisingelectrically controlled power means for driving the member at varyingspeeds in either of two opposed directions. an ampliiier circuitoperable to receive electrical signals and render them of a characterand magnitude suitable for controlling said power means, a rst controlmeans for governing move- -ment ofthe member through speed control ofsaid power means, a second control means including a rst Selsyn drivento have a movement corresponding to that of the member, a second Selsynadapted to be connected to said amplier circuit, a third Selsynmechanically connected with said second Selsyn, said first and saidthird Selsyns having connection to a common voltage source, a manualcontrol element, a clutch for coupling or uncoupling said last namedmanual control element from said second Selsyn, a switch vfor connectingsaid first control means to said amplier and said rst Selsyn to saidthird Selsyn and in the alternative connecting said second Selsyn tosaid amplifier and said i-lrst Selsyn to said second Selsyn, andelectrical means for simultaneously controlling said clutch and saidswitch.

" 4'. A control system for governing the move- Yment` of a membercomprising electrically conutrolledppower means for driving the memberat :varying speeds in either of two opposed directions, an amplifiercircuit operable to receive electrical signals and render them of acharacter and a magnitude suitable for controlling said power means, arst control means for governing move- -inent of the member comprisingmanually controlled signal generating means operable to gen- .erate amain signal of opposed character and adjustable magnitude, and means forgeneratinga pilot signal varying in magnitude and character with thespeed and direction of movement of the member,l said pilot signalgenerating means being connected in the input to said amplifiercircuitin inverse feed-back, 4asecond control means for `governing themovement ofthe member comprising a rst Selsyn mechanically driven tohave a movement corresponding to that of the member, a secondSelsyn'adapted to be connected to said amplifier circuit, a third Selsynmechanically connected with said second Selsyn, said rst and said thirdSelsyns having connection to a common voltage source, a manual controlelement, a clutch for coupling or uncoupling said last named manualcontrol element and said second Selsyn, a switch for connecting thesignal generating means of said first control means to said amplilierand said rst Selsyn to said third Selsyn and, in the alternative,connecting said second Selsyn to said amplier and said rst Selsyn tosaid second Selsyn, and electrical means for simultaneously controllingsaid clutch and said switch to couple said second Selsyn and its manualcontrol element when said second Selsyn is electrically connected tosaid amplifier.

5. A fine position signal-generating system for selective control of asignal controlled power system for moving a member, such power systemincluding power means for driving such a member at varying speeds and ineither of two opposed directions in correspondence to sense andmagnitude of a control signal, and a second signalgenerating systemconnectible to and disconnectible from said power means manuallyactuable to produce a signal of selectable sense and magnitude; saidfine position control system comprising a Selsyn generator lmechanicallyconnected with said power means for operation in correspondence to driveof such a member, a Slsyn control transformer manually operable to aposition representative of a required position of such member, a Selsynmotor mechanically coupled to said control transformer, and switch meansfor selectively coupling said motor or said control transformer to saidgenerator respectively to maintain said transformer in positionalcorrespondence with such a driven member or to generate a signalrepresentative of error between an actual position of such a drivenmember and a required position represented by the position of saidcontrol transformer, and means for connecting the output of said controltransformer to said power means when said second signal-generatingsystem is disconnected from it.

6. A control system for covering the movement of a member, comprisingelectrically controlled power means for driving the member at varyingspeeds in either of two opposite directions, an amplifier circuitoperable to receive electrical signals and condition them forcontrolling said power means, a rst control means for governing movementof the member through speed control of said power means; a secondcontrol means for governing the Vmovement of the member throughVposition control of said power means, a position operable when coupledelectrically with said rst l device and mechanically with said seconddevice to maintain the latter in step with the member;

fa selector system including switching means operable to selectivelyelectrically couple either said second or said third electrical devicewith said first electrical device and simultaneously with vrtomechanically couple said secondD electrical device with said secondcontrol means or with said third electrical device, and a selectorarranged to simultaneously operate said switching means and saidcoupling devices to selectively electrically couple said second devicewith said amplifier circuit and first electrical device andsimultaneously mechanically couple it with said second control means anduncouple it from said third electrical device or to couple said thirddevice electrically with said first device and mechanically with saidsecond device and to mechanically couple and uncouple said secondelectrical device with and from the third electrical device and secondcontrol means respectiveiy, and means operable by said selector systemto connect and disconnect said rst control means to and from theamplifier circuit respectively as the second electrical device isdisconnected from and connected with it.

HERBERT ZIEBOLZ. PAUL GLASS` REFERENCES CITED The following referencesare of record in the file of this patent:

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